Duplex stainless steel tubes having the composition defined hereinafter are used in a wide variety of applications in which they are subjected to corrosive media as well as substantive mechanical load. During the production of such duplex stainless steel tubes, different process parameters have to be set correctly in order to obtain a steel tube having the desired yield strength. Process parameters that have been found to have important impact on the final yield strength of the material are the following: degree of hot deformation, degree of cold deformation and ratio between tube diameter and tube wall reduction during the process in which a hot extruded tube is cold rolled to its final dimensions. These process parameters have to be set with regard to the specific composition of the duplex stainless steel and the desired yield strength of the duplex stainless steel tube.
Up to this point, prior art has relied upon performing extensive trials in order to find process parameter values resulting in the achievement of a target yield strength of duplex stainless steel tubes. Such trials are laborious and costly. Therefore, a more cost-efficient process for determining process parameters crucial to the yield strength is desirable.
EP 2 388 341 suggests a process for producing a duplex stainless steel tube having a specific chemical composition, wherein the working ratio (%) in terms of reduction of area in the final cold rolling step is determined for a predetermined targeted yield strength of the tube by means of a given formula that also includes the impact of certain alloying elements on the relationship between working ratio and targeted yield strength.
The present disclosure aims at presenting an alternative process for manufacturing a tube of a duplex stainless steel by setting a Q-value, as defined hereinafter, and a cold reduction R, as defined hereinafter, in order to achieve a targeted yield strength of the produced duplex stainless steel tube, and thereby improving the total manufacturing efficiency.